This invention relates to an illumination optical system and an exposure apparatus having the same. The present invention is suitably usable in the manufacture of various devices such as a semiconductor device (e.g., IC or LSI), an image pickup device (e.g., CCD), a display device (e.g., liquid crystal panel) or a magnetic head, for example. More specifically, it is suitably applicable in a step-and-repeat type or step-and-scan type exposure apparatus, used in a lithographic process, for illuminating a pattern of a first object such as a reticle with slit-like light of an arcuate shape and for projecting it onto a second object such as a wafer through a projection optical system.
The density of integration of a semiconductor device such as an IC or LSI has been increased more and more and, as a projection exposure apparatus which plays a major role in semiconductor wafer microprocessing, there have been proposed a unit-magnification projection exposure apparatus (mirror projection aligner) wherein a mask and a photosensitive substrate are exposed while being scanned relative to a unit-magnification mirror optical system having an arcuate-shape exposure region, and a reduction projection exposure apparatus (called a stepper) wherein a pattern image of a mask is formed on a photosensitive substrate through a dioptric optical system and the photosensitive substrate is exposed thereby in a step-and-repeat method.
The size of a chip pattern of a single semiconductor device is increasing, and thus enlargement of the picture size has been required for a projection optical system so that a large-area pattern can be printed on a photosensitive substrate.
In consideration of these requirements, many proposals have recently been made on a scanning projection exposure apparatus of a step-and-scan type by which a high resolution and a wide picture size are attainable.
In such scan type exposure apparatuses, a pattern on a reticle surface is illuminated with slit like light. The pattern thus illuminated with the slit-like light is transferred to a wafer through a projection system (projection optical system) and in accordance with a scan motion.
In one scan type exposure apparatus, the scan exposure is made by use of slit-like light of an arcuate shape. In this type, there is a projection optical system intervening between a first object, having a pattern to be transferred, and a second object to which the pattern is to be transferred. The exposure process is performed by use of only a particular abaxial image point. The projection optical system has an optical axis, and its optical characteristic is revolutionally symmetrical with respect to the optical axis. Thus, in the exposure method based on an abaxial image point, slit-like light of an arcuate shape is used.
Generally, collecting the light to an arcuate region is very difficult. In the past, a light source having a light emitting surface of an arcuate shape was developed. In another proposal, as shown in FIG. 5, an arcuate area is extracted out of a region 51, being illuminated in an oblong shape, by use of an aperture member 50 having an arcuate opening. However, development of a light source having an arcuate-shape light emitting surface in the former case is difficult to accomplish if the light is in a short wavelength region such as the DUV (Deep Ultraviolet) region. The arcuate shape extraction in the latter case involves a disadvantage of a very low light utilization efficiency.
It is an object of the present invention to provide an illumination optical system by which slit-like light of an arcuate shape can be provided easily and with a good light utilization efficiency.
It is another object of the present invention to provide an illumination optical system by which arcuate-shaped illumination can be performed with a good light utilization efficiency by use of an ordinary discharge tube such as an ultra-high pressure Hg lamp or a laser light source (and without use of a special light source), while satisfying a predetermined illumination condition.
It is a further object of the present invention to provide an exposure apparatus of a proximity type, of a step-and-repeat type or of a step-and-scan type, having such an illumination optical system, which can be suitably used in the manufacture of semiconductor devices, for example.
In accordance with an aspect of the present invention, there is provided an illumination optical system, comprising: a first beam shape changing optical system for transforming a light, supplied from a light source, into a slit-like light of an oblong shape; and a second beam shape changing optical system for transforming the slit-like light of an oblong shape into a slit-like light of an arcuate shape, said second beam shape changing means having a prism element; wherein said illumination optical system can be used to illuminate a surface, to be illuminated, with the use of the slit-like light of arcuate shape.
In accordance with another aspect of the present invention, there is provided an exposure apparatus, comprising: an illumination optical system as recited above, for illuminating a mask having a pattern formed thereon; and a projection optical system for projecting the pattern of the mask onto a wafer.
In accordance with a further aspect of the present invention, there is provided a device manufacturing method, comprising the steps of: applying a resist to a wafer; exposing the wafer having the resist applied thereto, with a pattern of a mask by use of an exposure apparatus as recited above; and developing the wafer having the pattern transferred thereto.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.